Atomic‐Scale Cation Partitioning Links Reaction‐Product Chemistry to Molten‐Silicate Passivation in Rare‐Earth Tantalates
Zeyu Chen, Yiling Huang, Fan Peng, Wei Zheng, Xuemei Song, Yaran Niu, Yi ZengABSTRACT
Molten silicates can be immobilized by protective reaction products or continue to penetrate oxide ceramics, but the structural features that distinguish these pathways remain unclear. Here we examine CMAS reactions with RETa 3 O 9 and connect crystallographic cation partitioning in corrosion products with passivation across rare‐earth chemistry, melt composition, and multicomponent design. EuTa 3 O 9 forms a durable bilayer comprising a dense AX 2 O 6 barrier and a cation‐sequestering B 2 Y 2 O 7 layer; a related consumption–barrier architecture persists in Fe‐rich lunar‐ and Martian‐regolith analogue melts. Across 11 RETa 3 O 9 compositions, rare‐earth size acts as a structural descriptor for access to AX 2 O 6 ‐, B2Y2O 7 ‐, and CZO 4 ‐containing reaction pathways. Using this relationship as a design constraint, Eu‐centred high‐entropy RETa 3 O 9 compositions retain resistance to bulk penetration while reducing thermal conductivity. HEC‐2 forms an 84.4 µm reaction layer after 100 h at 1300°C and exhibits an 8.3% lower calculated effective thermal conductivity than EuTa 3 O 9 at 1200°C. These results link reaction‐product chemistry to mechanism‐constrained composition design for high‐temperature protective ceramics.